Remarks:
1. This tutorial describes how to install gnu parallel (2014.07.22) from source on a Ubuntu 14.04 LTS PC, but it can be easily adapted for other versions of gnu parallel and/or Linux distributions.
2. For one-line solutions please see this comment and the subsequent reply.

Step 1: Create a new script

All required steps to install gnu parallel (2014.07.22) will be written in a script called GnuParallelSetup.sh (assuming you do not have a file with that name in the current folder already).

To create the file write on the command line the following (excluding the “$” symbol):$ touch GnuParallelSetup.sh

Step 2: Install dependencies and gnu parallel

Open the script using your favourite text editor. Assuming this is vi(m) write on the command line the following (excluding the “$” symbol):$ vim GnuParallelSetup.sh

Next write the contents of the script (i.e. copy and paste the text below into the script):